Structural honeycomb materials



Jan. 19, 1965 D. D. WHITE ETAL' STRUCTURAL. HONEYCOMB MATERIALS FiledMarch 14, 1962 In entori asmoma nsvmm wmrz. PETER mm THWAITEs 21wGEOFFREY RONALD J'UDD B M QM A tlorney$ United States Patent Wee3,166,456 STRUCTURAL HONEYCOMB MATERIALS Desmond Deverell White,Radlett, Peter .lohn Thwaites, London, and Geofirey Ronald Judd, Ware,England, assignors to Dufaylite Developments Limited, London, EnglandFiled Mar. 14, 1962, Ser. No. 179,703 Claims priority, application GreatBritain Mar. 22, 1961, 10,441/61 3 Claims. (Cl. 156-497) The presentinvention relates to the production of structural honeycomb material ofthe expandable type from bibulous sheet material, for example paper,using a wet adhesive. In its expanded form the material is widely usedas the core of sandwich structures on account of its high strength toWeight ratio and favorable cost.

Basically the production of the material for expansion involves securingtogether layers of sheet material in face to face contact by parallelbands of the adhesive positioned such that the bands at one face of anylayer are staggered with reference to the bands at the other facethereof.

Various methods of bringing the layers and the adhesive automaticallyinto the required relationship have been proposed but all have exhibiteddisadvantages. Except for production of inferior quality, arrangementsmust, in practice, be made for giving accurate registration of the wetadhesive between the layers on first contact thereof and preventingsubsequent movement of the layers while the adhesive is wet. Sucharrangements have hitherto involved the provision of machinery which hasbeen wasteful in operation or whose rate of output has beendisappointing in relation to capital cost, space occupied or maintenancerequirements.

One type of method which has been proposed involves folding a continuousweb of the sheet material bearing the wet adhesive in such a manner asto produce a stack in which the layers are formed by folding thematerial backwards and forwards and it is with this type of method thatthe present invention is concerned. To provide apparatus for merelyfolding material backwards and forwards is a simple matter but majordifiiculties arise from the need to accomplish accurate folding in thepresence of the wet adhesive. Once a pair of layers has been broughttogether with the adhesive between them relative movement must beprevented, otherwise the outline of the adhesive is lost and the qualityof the product spoiled. Thus the first contact of one layer with thenext must be made accurately in the finally required position, nosubsequent correction being possible. The folding mechanisms which havebeen proposed to ensure satisfactory results have been elaborate innature and low in output or inflexible or wasteful in operation. A highfolding speed has been obtainable only by giving the layers such smalldimensions between folds as to enable the material to be produced onlyin or near its finally required thickness, taken in the axial directionof the cells, and so has not enabled the rate of production to beeffectively multiplied by subsequently forming the stack into a largenumber of slices. Because of its multiplying effect, its dimensionalaccuracy, the ease with which the thickness can be varied as well as thelow trimming waste per volume of product, slicing is always attractive.Moreover, the apparatus is suitable for serious commercial use, onlywith adhesives which can be dried before the layers are contactedtogether and subsequently activated in a final step of the process. Thewet adhesives with which the invention is concerned are preferred in theart and adopted where possible in spite of their difi'lculties.

Modern mechanized methods of forming a stack for slicing by piling uppre-cut sheets with wet adhesive appropriately positioned can inpractice be made to operate 3,166,455 Patented Jan. 19, 1965 at about 20sheets per minute. Taking the number of slices as about 40, which istypical, it will be seen that the folding rate required to produce thesame product directly in the required thickness and at the same speedwould be as high as 800 folds per minute.

One form of the folding method which has been proposed involves feedinga web of paper printed with glue lines on both sides verticallydownwardly towards a support and folding the material upon the supportby the action of arms or other mechanical members operating from theopposite ends of the support in turn, the feeding and folding stepsbeing carried out at such relative speeds that there is always asufiicient length of suspended material to permit its being foldedwithout appreciable drag thereon. The speed of this method depends uponthe speed of the mechanical members which has to be limited in order toavoid tearing the suspended material. Moreover, the folds obtained tendto be bulky rather than sharp with the result that pronounced bulgesbuild up at the ends of the block and considerable trimming waste isincurred.

In accordance with the present invention there is provided a method forthe production of structural honeycomb material which comprises applyingwet bands of adhesive to both faces of a web of bibulous sheet materialin positions such that the bands applied to one face are staggered withreference to the bands applied to the other face, feeding the webdownwardly towards a support and folding it backwards and forwards uponthe support so that it is accumulated upon the support in the form of astack of layers which are adhered together by the wet hands and areinterconnected at their ends, characterized in that the web is formed atequidistant intervals along its length and thereby divided into discretesheet sections, with hinge formations, conveniently sets of colineartransverse slits which leave the sheets joined together by interveningsections of intact material, and is fed dodwnwardly to the support at arate of feed such that it swings freely backwards and forwards under thereaction of the support and is accumulated in the form of a stack oflayers in which each layer is constituted by one of said sheets and thesheets are joined together by folds at the position of the hingeformations.

By the foregoing method the folding of the Web is obtained, withoutmechanical interference therewith, in a rapid and satisfactory manner.Even though the bands of adhesive are wet during the descent and foldingof the web, accurate registration of the bands in the folded material isobtained.

Under the free swinging conditions each sheet is guided accurately intoposition as it descends by its hinged attachment to the preceding andsucceding sheets. There are no impulsive disturbances producing shockwaves or other sources of distortion. The movement of the sheet materialduring the descent closely resembles a wave motion with no significantfolding at the hinge formations until the particular sheets which theydefine are being laid on the support. Obviously the form of this motionis rendered complex by air-damping and by the discontinuities introducedby the hinge formations where the sheets are attached one to the other.As a rough guide it may be noted that the maximum rate of free swingapproximates to the rate of a simple pendulurn whose length equals thedistance of free descent. The system would be too complex, even in theabsence or air-damping, for any precise relationships to be formulatedbut the required motion is readily achieved by adjusting the rate offeed of the web and/ or the distance of its descent to the support.

The rate of output depends upon the frequency of free swinging, and forconvenient dimensioning of the layers a speed of 30 layers per minute istypical.

Because the folding of the web is produced without the aid of mechanicalcomponents acting intermittently the apparatus required is simple andthe method is attractively economical for thisreason alone. In additionthe method permits a procedure which has never been applicableheretofore. Thus the support may be mounted for horizontal movement inthe direction of the length of the accumulated sheets sothat, on suchmovement, the material accumulates in a fresh stack by the side of thefirst which may be removed Without interrupting the feeding of the web.This is especially advantageous when the stacks are required to haveonly a small number of layers, as in the manufacture of honeycomb oflarge cell size for packaging purposes. Additionally the operator isenabled to withdraw the accumulated material for consolidation underpressure at frequent intervals and without interrupting the process,thereby increasing the quality of the product by minimizing the timebetween laying the wet adhesive and consolidation.

The following description in which reference is made to the accompanyingdrawing is given by way of illustration.

In the drawing:

FIG. 1 is a diagrammatic side elevation of an apparatus used in themethod of the invention,

FIG. 2 shows the arrangement of the slits in the web, and

FIG. 3 shows a portion of the slit web after the application of adhesivethereto.

A Web 1 of paper, e.g. kraft paper or the thin cardboard known aschipboard, is drawn from a supply roll 2 to pass between a pair ofslitting rollers 3 which operate to provide hinge formations in the setsof colinear transverse slits 4 dimensioned to leave narrow intact hingeportions 5 of the web material therebetween. After such slitting the webmay be regarded as a series of sheets 6 interconnected by the hingeportions 5.

The web passes downwardly through printing heads 7 and 8 to be printedwith parallel longitudinally extending bands a and b of wet adhesive,the bands a printed on one side lying between the bands b printed on theother side. It is preferably arranged, as shown in FIG. 3, that thehinge portions 5 lie on some of the adhesive bands while other adhesivebands pass through the slits.

The web leaving the lower printing head 8 descends to a horizontalsupport 9 and accumulates thereon in a stack of layers which are joinedat their ends 10 and 11 by the hinge portions 5. During accumulation ofthe stack the suspended material 12 swings backwards and forwards in thedirection shown by the arrows, the rate of feed of the web beingadjusted so that the swinging takes place at the natural frequency whichis governed by the vertical distance from the lower printing head 8 tothe support 9.

The suppont 9 is mounted on rails 13 and after a chosen number of layershas accumulated, the support is moved rapidly by air cylinder 14,without interrupting the feeding of the web, to bring a second support 9into position below the printing heads for the reception of furtherlayers. The material on support 9 is removed and consolidated underpressure for conventional slicing in the guillotine.

Intermittently acting air nozzles 15 are provided to 4 initiate theswinging of the web on starting the apparatus, but are not essential.

The method described herein is especially advantageous over methodsinvolving the use of a rotary former when applied to manufacture fromchipboard or other material whose thickness causes the waste,characteristic of such methods, to become substantial. The trimming lossinvolved in squaring the end of the stack is trivial.

It will be understood that the foregoing description of one example ofthe method, given with reference to the drawing, is provided forpurposes of illustration only.

We claim:

1. A method for producing structural honeycomb material consisting informing rows of colinear spaced apart slits transversely of a flat webof bibulous sheet material, spacing said rows of slits at equalintervals along the length of said web dividing said web into sheetsections, spacing the slits in each of said rows thereof providing hingesections of intact material between each pair of said slits joiningadjacent sheet sections, applying wet bands of adhesive to both faces ofsaid web at positions thereon such that the bands applied to one faceare staggered with reference to the bands applied to the other face ofsaid web, feeding said web of bibulous sheet material in a downwarddirection onto a receiving support, accumulating said web on saidreceiving support in stacks of superimposed layers in which each layeris constituted by one of said sheets and which layers are joinedtogether by their hinge sections folded under the reaction of each sheetsection reaching the material therebeneath on said receiving support,bonding said layers together in their stacked condition by said adhesiveand slicing said bonded stacked layers into expandable sections.

2. A method for producing structural honeycomb material as claimed inclaim 1 including controlling the rate of speed at which said webtravels during its downward feeding imparting a free lateral swing tosaid web folding said hinge sections as they reach the end of each swingof said web.

3 A method for producing structural honeycomb material as claimed inclaim 1 in which said sheet material is chipboard.

References Cited by the Examiner UNITED STATES PATENTS 2,581,421 1/52Lombard et a1. 156-197 2,610,934 9/52 Steele 156-197 2,619,444 11/52Grantham 156197 2,663,434 12/53 Pierce 21416.6 2,684,107 7/54 Schultz156-204 2,865,639 12/58 Gillette et a1. 156-204 2,897,874 8/59 Stalegoet a1 l56-197 3,074,839 1/64 May et a1 l56--197 3,123,269 3/64 Morley etal. 156474 FOREIGN PATENTS 659,075 10/51 Great Britain.

723,621 2/55 Great Britain.

865,813 4/61 Great Britain.

EARL M. BERGERT, Primary Examiner.

1. A METHOD FOR PRODUCING STRUCTURAL HONEYCOMB MATERIAL CONSISTING INFORMING ROWS OF COLINEAR SPACED APART SLITS TRANSVERSELY OF A FLAT WEBOF BIBULOUS SHEET MATERIAL, SPACING SAID ROWS OF SLITS AT EQUALINTERVALS ALONG THE LENGHT OF SAID WEB DIVIDING SAID WEB INTO SHEETSECTIONS, SPACING THE SLITES IN EACH OF ROWS THEREOF PROVIDING HINGESECTIONS OF INTACT MATERIAL BETWEEN EACH PAIR OF SAID SLITS JOININGADJACENT SHEET SECTIONS, APPLYING WET BAND OF ADHESIVE TO BOTH FACES OFSAID WEB AT POSITIONS THEREON SUCH THAT THE BANDS APPLIED TO ONE FACEARE STAGGERED WITH REFERENCE TO THE BANDS APPLIED TO THE OTHER FACE OFSAID WEB, FEEDING SAID WEB OF BIBULOUS SHEET MATERIAL IN A DOWNWARDDIRECTION ONTO A RECEIVING SUPPORT, ACCUMULATING SAID WEB ON SAIDRECEIVING SUPPORT IN STACKS OF SUPERIMPOSED LAYERS IN WHICH EACH LAYERIS CONSTITUTED BY ONE OF SAID SHEETS AND WHICH LAYERS ARE JOINEDTOGETHER BY THEIR HINGE SECTIONS FOLDED UNDER THE REACTION OF EACH SHEETSECTION REACHING THE MATERIAL THEREBENEATH ON SAID RECEIVING SUPPORT,BONDING SAID LAYERS TOGETHER IN THEIR STACKED CONDITIONS BY SAIDADHESIVE AND SLICING SAID BONDED STACKED LAYERS INTO EXPANDABLESECTIONS.